The invention relates to a needle for carrying out operations with flexible cords, roves or threads.
A needle of this type finds its application in particular in the field of the fabrication of armatures by a multidirectional weaving. Such armatures are employed, after impregnation with a suitable binder and polymerization, for producing structural units of a composite material which can be subjected to very great mechanical and thermal stresses.
A particular purpose of the invention is to permit the weaving of a structure which will comprise continuous fibers oriented in at least three directions generally perpendicular to one another.
The general principle of the weaving of such structures consists in disposing fibers in two directions between and around a third direction materialized either by rigid rods which are for example metal rods, or by taut roves, or by rods of composite material constituted by impregnated, hardened and calibrated roves.
A known technique for producing such a structure consists in "depositing" the fibers by means of hollow needles which receive and convey the fibers through the network and then abandon them upon a reverse movement, these fibers being maintained taut in their forward travel by maintaining elements.
In the known technique, the fibers are conveyed in hollow needles whose elongated body is a stem of substantially rectangular flattened section whose reduced width permits the passage between the metal rods or taut roves.
The hollow needles employed in this technique must be sufficiently rigid to avoid deviating from their direction under the effect of forces applied thereto which are due to the driving of the fibers in such manner as to avoid deteriorating the network of vertical rods and deteriorating the fibers, they convey. The needles must be easy to employ when preparing the device before the weaving, in particular permit the introduction of the fibers in the stem.
The known needles are made from a tube having a thin wall which is flattened until there is obtained the thickness which is compatible with the width of the meshes of the network, the end of the tube being cut on the bevel from which burrs are carefully removed.
These needles present many drawbacks. It is particularly difficult to thread the threads or the fibers in their narrow and long body, for example 300 to 500 mm. There is a risk of a clogging of the fibers in the tube by accumulation of small particles or fibrillae which slow down the weaving process. It has also been found that there is a degradation of the fiber at the stage of the penetration into the network owing to an exaggerated bending of the fiber at the bevelled free end of the needle, in particular in the case of the use of fragile fibers having a high modulus of elasticity. This drawback is particularly harmful since it affects the final mechanical characteristics of the woven product. Lastly, owing to their fragility, the hollow needles are often destroyed by buckling.